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Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2- A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (b) 25Hz (c) 5Hz ()2Hz (a) 50Hz 3- The efficiency of 3-phase induction motor is about (a) 100% Ad (C) 80-90% (c) 50-60% (d) Less than 50% ........... (b) Two parallel windings in stator 4- A double squirrel-cage induction motor has (a) Two series winding in stator (e) Two parallel winding in rotor (d) Two rotors moving in opposite direction The rotor slots are slightly skewed in squirrel cage induction motor to ---------- (6) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication ...... (a) Increase the strength of rotor bars (c) Economize on the copper to be used 6- Stable operation of an induction motor is (a) Between zero slip and unity slip (c) Between 6.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (c) Very low flux density in rotor parts (b) Between zero slip and slip corresponding to maximum torque (U) Between slip corresponding to maximum torque and unity slip (b) Very low emf induced in the rotor (d) Constant magnitude of flux linking the rotor core 8- The starting current of a 3-phase induction motor is about of its full load rated current (a) Half (b) Twice (e) 5 to 7 times 9- During plugging of an induction motor a) Phase sequence is reversed (e) One phase is open circaited (d) 8 to 10 times (b) A de source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For: any capacity

Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2- A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (b) 25Hz (c) 5Hz ()2Hz (a) 50Hz 3- The efficiency of 3-phase induction motor is about (a) 100% Ad (C) 80-90% (c) 50-60% (d) Less than 50% ........... (b) Two parallel windings in stator 4- A double squirrel-cage induction motor has (a) Two series winding in stator (e) Two parallel winding in rotor (d) Two rotors moving in opposite direction The rotor slots are slightly skewed in squirrel cage induction motor to ---------- (6) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication ...... (a) Increase the strength of rotor bars (c) Economize on the copper to be used 6- Stable operation of an induction motor is (a) Between zero slip and unity slip (c) Between 6.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (c) Very low flux density in rotor parts (b) Between zero slip and slip corresponding to maximum torque (U) Between slip corresponding to maximum torque and unity slip (b) Very low emf induced in the rotor (d) Constant magnitude of flux linking the rotor core 8- The starting current of a 3-phase induction motor is about of its full load rated current (a) Half (b) Twice (e) 5 to 7 times 9- During plugging of an induction motor a) Phase sequence is reversed (e) One phase is open circaited (d) 8 to 10 times (b) A de source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For: any capacity

Delmar's Standard Textbook Of Electricity
Delmar's Standard Textbook Of Electricity
7th Edition
ISBN:9781337900348
Author:Stephen L. Herman
Publisher:Stephen L. Herman
Chapter32: Three-phase Motors
Section: Chapter Questions
Problem 8RQ
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Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2- A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (b) 25Hz (c) 5Hz ()2Hz (a) 50Hz 3- The efficiency of 3-phase induction motor is about (a) 100% Ad (C) 80-90% (c) 50-60% (d) Less than 50% ........... (b) Two parallel windings in stator 4- A double squirrel-cage induction motor has (a) Two series winding in stator (e) Two parallel winding in rotor (d) Two rotors moving in opposite direction The rotor slots are slightly skewed in squirrel cage induction motor to ---------- (6) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication ...... (a) Increase the strength of rotor bars (c) Economize on the copper to be used 6- Stable operation of an induction motor is (a) Between zero slip and unity slip (c) Between 6.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (c) Very low flux density in rotor parts (b) Between zero slip and slip corresponding to maximum torque (U) Between slip corresponding to maximum torque and unity slip (b) Very low emf induced in the rotor (d) Constant magnitude of flux linking the rotor core 8- The starting current of a 3-phase induction motor is about of its full load rated current (a) Half (b) Twice (e) 5 to 7 times 9- During plugging of an induction motor a) Phase sequence is reversed (e) One phase is open circaited (d) 8 to 10 times (b) A de source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For: any capacity
Transcribed Image Text:Choose the correct answer: 1- In an induction motor, no-load slip is generally- (a) Less than 1% (b) 2% (c) 4% (d) 5% 2- A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be-------- (b) 25Hz (c) 5Hz ()2Hz (a) 50Hz 3- The efficiency of 3-phase induction motor is about (a) 100% Ad (C) 80-90% (c) 50-60% (d) Less than 50% ........... (b) Two parallel windings in stator 4- A double squirrel-cage induction motor has (a) Two series winding in stator (e) Two parallel winding in rotor (d) Two rotors moving in opposite direction The rotor slots are slightly skewed in squirrel cage induction motor to ---------- (6) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication ...... (a) Increase the strength of rotor bars (c) Economize on the copper to be used 6- Stable operation of an induction motor is (a) Between zero slip and unity slip (c) Between 6.5 slip and 0.95 slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (c) Very low flux density in rotor parts (b) Between zero slip and slip corresponding to maximum torque (U) Between slip corresponding to maximum torque and unity slip (b) Very low emf induced in the rotor (d) Constant magnitude of flux linking the rotor core 8- The starting current of a 3-phase induction motor is about of its full load rated current (a) Half (b) Twice (e) 5 to 7 times 9- During plugging of an induction motor a) Phase sequence is reversed (e) One phase is open circaited (d) 8 to 10 times (b) A de source is connected to stator (d) Power is fed back to mains 10- Direct online (D.O.L.) starter is used for induction motors a)Less than 5 h.p. (b) Less than 10 h.p. (c) Greater than 10 h.p. (d) For: any capacity
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